1. Field of the Invention
The present invention relates to a ferrule block which is attached to an optical device module to optically couple to an optical fiber serving as a transmission line, and to an optical module using the same.
2. The Related Art of the Invention
A ferrule block is attached to an optical device module, which houses in its package an optical device for sending or receiving a light signal, to optically couple to an optical fiber serving as a transmission line, and is also referred to as a capillary block or a receptacle.
FIG. 1 shows a ferrule block 131 as an example of such a ferrule block. The ferrule block 131 primarily includes a substantially cylindrical ferrule block body 132 made of metal and a substantially cylindrical shell 133 made of metal which is provided at one end of the ferrule block body 132 so as to partly project therefrom.
At one end of the ferrule block body 132, one end of the shell 133 is press fitted and fixed. At the other end of the ferrule block body 132, a ferrule (capillary) 135 holding an optical fiber 134 in its center is fixed.
The ferrule block 131 is, in use, attached to a metal casing 136 of an electronic device so that the ferrule block body 132 is housed within the casing 136 and the one end of the shell 133 projects outside the casing 136. In FIG. 1, the left side of the casing 136 shows an inside of the casing 136 and the right side of the casing 136 shows an outside of the casing 136, wherein the other end of the optical fiber 134 is optically coupled to an optical device (not shown).
In this state, an optical connector not shown, which includes an optical fiber serving as a transmission line and a ferrule holding the optical fiber, is further connected to the one end of the shell 133. This allows the optical device, the optical fiber 134, and the optical fiber of the optical connector to be optically coupled.
Since the shell 133 is metallic, it is inexpensive and can be press fitted into the ferrule block body 132 even if a tolerance between an inside diameter of the ferrule block body 132 and an outside diameter of the shell 133 is loose.
Meanwhile, there is an earlier art relating to the invention disclosed in the present application (refer to Japanese Unexamined Patent Publication No. 9-304652 (FIG. 1)).
However, since the shell 133 is metallic and moreover the shell 133 projects outside the casing 136, the ferrule block 131, when incorporated in an electronic device which operates under low-frequency signals, does not present any problems, but when incorporated in an electronic device which operates under high-frequency signals, the ferrule block 131 has a problem that the shell 133 functions as an antenna and tends to pick up an electromagnetic noise e1 from the outside during the operation of the electronic device. The ferrule block 131 also has a problem that it is easy to emit an electromagnetic noise e2 to the outside.
In particular, a recent optical transceiver has a very fast transmission speed of 10 Gbps or more. Accordingly, incorporating the ferrule block 131 into such a transceiver will significantly increase the influence of the electromagnetic noises e1 and e2.